Device for measurement of liquid level or volume of liquefied gases



WERRCH O! \May 1, 1962 c. R. WEISEND 3,031,887 DEVICE FOR MEASUREMENT OFLIQUID LEVEL OR VOLUME OF LIQUEFIED GASES Original Filed Aug. 10, 1959mm m w m S C m m 4 P W 2 r 1 J1 @m W m m wsv 8 M w MAR I. RNL G EEU m SP T E M H R E T /T IIIIII'IIIIII INVENTOR.

CHARLES R. WEISEND W 7 ATTORNEY.

United States Patent 3,031,887 DEVICE FOR MEASUREMENT OF LIQUID LEVEL ORVOLUME OF LIQUEFIED GASES Charles R. Weisend, Columbus, Ohio, assignorto Herrick gifillohnston, Inc., Columbus, Ohio, a corporation ofContinuation of application Ser. No. 832,619, Aug. 10,

1959. This application Dec. 1, 1960, Ser. No. 73,146

3 Claims. (Cl. 73-295) This is a continuation of United States patentapplication Serial No. 832,619, filed August 10, 1959, and nowabandoned.

The present invention relates to level or volume indicators forcryogenic applications. As stated in Cryogenie Engineering, Scott (VanNostrand, New York, 1959), at page 243, Many types of level indicatorshave been used in Dewars and other cyrogenic equipment. These aresummarized in Scotts work at pages 243-247 and illlustra-te the need foran economical and accurate indicator. The present invention is intendedto serve that need and this is accordingly its principal object.

The present invention is based on the observation that when a capillarycontaining gas is partially immersed in a cryogenic liquid, the gas isliquefied until its level and the liquid level in the container areequalized.

Now if gas contained in the capillary is in communication with a gasreservoir, maintained under constant temperature conditions, then thepressure in this gas reservoir is a measure of the liquid level in theDewar or cryogenic liquid storage vessel. For example, if the liquidlevel in the storage vessel is high, then more of the gas in thecapillary is liquefied than would be the case if the liquid level islow. In the former case, the pressure drop in the gas reservoir due tothe liquefication of gas in the capillary is considerable. In the lattercase less gas in the capillary is liquefied and the pressure drop in thegas reservoir is less.

Stating this phenomenon in other words, the heat loss of the gascontained in the capillary to the surrounding cryogenic liquid in thestorage vessel is sulficient to liquefy this gas in the capillary untilthe liquid levels in the storage vessel and the capillary are equalized.This liquefaction is accompanied by pressure changes in the capillaryand in the accompanying gas reservoir. This pressure is measured by anappropriate conventional pressure-measuring device, correlated to theheight of the liquid level in the capillary and calibrated in terms ofliquid level in the storage vessel. The device is also suitable tomeasure liquid volume in any storage vessel or closed system.

For a better understanding of the invention, together with otherobjects, advantages and capabilities thereof, reference is made to theappended description of the accompanying drawings, in FIG. 1 of whichthere is illustra-ted a system containing a liquid level measuringdevice in accordance with the present invention, and in FIG. 2 of whichthere is illustrated, also in section, an alternative form of liquidlevel indicator having a helical type of capillary.

In the drawings:

Reference numeral 10 in FIG. 1 is indicative of a cryogenic liquidstorage vessel or Dewar, for example. Immersed in vessel 10 is my novelindicating vehicle. It comprises a metallic sheath 11. Axially disposedwithin the sheath and suitably electrically insulated therefrom isheater 13, energized from an adjustable source of electric current 21.Mounted on and efiectively in thermal contact with the sheath 11 is agas capillary 14 which communicates, as by pipe 15, fitting 16, and pipe17, with a gas reservoir 18.

In operation, the gas in capillary 14 liquefies up to the levelindicated by the reference numeral 19, so that it is equated to theliquid level of the surrounding cryogenic liquid 20. The operation ofheater 13 is such as to assure that gas in the capillary above the level19 remains vaporized. The wall of the capillary could of course be usedfor that purpose. The heater prevents the rise of liquid level in thecapillary above the level of the liquid in the storage vessel, whichundesired rise could be caused by the capillary action or by loss ofheat to the stored liquid in the storage vessel over and above the lossinvolved in equating level 19 to level 20.

The fact that the liquid in the capillary is equated to the liquid levelof the surrounding liquid furnishes an excellent basis for themeasurement of level indication. That is to say, the volume of gas inthe system 14, 15, 16, 17 and 18 is predetermined. When cryogenic liquidis placed in the storage vessel 10 there is a great loss of gas volumeand pressure in that system and accordingly the measurement of levelindication is quite sensitive, a small change in liquid level producinga great change in the pressure measurement at the gas reservoir. Theefficacy of these pressure changes as a measure of level of the liquidin the storage vessel depends of course on maintenance of consistancy oftemperature at gas reservoir 18, and this can be accomplished by athermostat 23 shown in block form.

The level measurement is made by pressure indicating device 24 suitablycalibrated in terms of liquid level in the storage vessel 10.

It will be understood that suitable solder seals 25, 26, 27 and 28 areprovided as required.

The capillary 14 is straight in the FIG. 1 embodiment which is wellsuited to liquid level measurement. The FIG. 2 embodiment is identicalto that of FIG. 1 except that it uses a helically wound capillary 14.The helically wound capillary is preferable for liquid volumemeasurements because greater sensitivity can be achieved by increasingthe volume of the liquefied gas in the capillary. The storage vessel 10being of upright cylindrical form, the volume of stored cryogenic liquidchanges in the same ratio as the liquid level. Therefore, either astraight or helical capillary can be used as a volume indicator. Thiswould be true in any case where the volume of the stored cryogenicliquid is directly proportional to its height. On the other hand, if thestorage vessel is a cylinder in a horizontal position, then the volumeof stored liquid is not proportional to the height and a capillary 14'would be wound in a non-linear fashion with the turns close together atthe center and further apart at the top and bottom of the capillary.This for the reason that a small change in liquid level at. a zone nearthe bottom of the storage vessel means a small change in volume while acorresponding change in level near the median line of the vessel means alarge change in volume, for example. The helical capillary 14' can bewound in any manner suitable to indicate volume.

The pressure indicating device 24 may be either an absolute ordifierential pressure gauge. In the event that a difierential pressuregauge is employed, the pressure indicator may be returned to fitting 1'6and capillary 15 via a temperature compensation bulb 29 and a valve 30.When the temperature compensating bulb is used, a thermostat is notrequired.

The invention is believed to possess several advantages. First, it isextremely sensitive, a small change in the level of liquid in thestorage vessel being accompanied by a very large pressure change atindicator 24. Second, the indicating device 24 can be convenientlylocated at a point remote from the storage vessel and because of thisfactor and the sensitivity factor just mentioned, this indicator isparticularly suited to transducer systems.

Normally, the same gas is used in the capillary as in the storage vessel10.

To compensate for the temperature changes in the stored liquid due topressurization of the storage vessel 10, the minimum pressure in the gasreservoir 18 must be higher than the maximum pressure in the storagevessel.

While there have been shown and described what are at present consideredto be the preferred embodiments of the invention, it will be understoodby those skilled in the art that various changes and modifications maybe made therein without departing from the true scope of the inventionas defined in the appended claims.

I claim:

1. A level indicating device comprising a sheath to be inserted into aliquid to be measured, an electrical resistance heater mounted withinsaid sheath, a gas-containing capillary mounted on said sheath, a gasreservoir in communication with said capillary, said heater means beingutilized to equate the level of gas which liquefies in the capillary tothe level to be measured, pressure indicating means coupled to said gasreservoir to determine liquid level or liquid volume as a function ofthe pressure effect in the gas reservoir and capillary, and means formaintaining constant the temperature of said gas reservoir.

2. A level indicating device in accordance with claim 1 in which thecapillary is helically Wound.

3. A level indicating device comprising a sheath to be inserted into aliquid to be measured, an electrical resistance heater mounted withinsaid sheath, a gas-containing capillary mounted on said sheath, a gasreservoir in communication with said capillary, said heater means beingutilized to equate the level of gas liquefied in the capillary to thelevel to be measured, and pressure measuring means coupled to said gasreservoir to determine liquid level or liquid volume as a function ofthe pressure effect in the gas reservoir and capillary, said pressuremeasuring means being :a differential device associated in series with atemperature compensation bulb at the inlet and outlet ends of said .gasreservoir.

References Cited in the file of this patent UNITED STATES PATENTS

